THE COOPER UNION
Albert Nerken School of Engineering
Soil Mechanics Laboratory
Experiment No. 6 - Constant Head Permeability Test
To measure the coefficient of permeability of granular soil samples; and to study the relationship between the coefficient of permeability and: (a) relative density, (b) voids ratio.

 

1) "Soil Testing for Engineers" by T. W. Lambe; - Chapter VI.

2) "Engineering Properties of Soils and Their Measurements" - 4th edition by Joseph E. Bowles, Experiment No. 9.

3) A.S.T.M. Standards, 1994; (4.08) Designation D2434-68(1994)e1.

 

1) Constant head supply tank

2) Three constant head permeameters

3) Six porous stones

4) Triple beam balance (sensitive to 0.1 gm)

5) Stopwatch

6) Thermometer (sensitive to 1.0C)

7) Miscellaneous apparatus:

  1. Graduated cylinders
  2. Beakers
  3. Pan
  4. Spatula
  5. Wide-mouthed funnel

 

1) Completely brush out the permeameter and insert a porous stone into the bottom.

2) Measure the inside diameter of the permeameter and calculate the cross-sectional area of the permeameter. Record the area on Data Sheet (A).

3) Measure the distance between the piezometer outlets.  Record this distance on Data Sheet (A).

4) Prepare the sample following the following procedures:

  1. 100% Relative Density
    1. Weigh a pan filled with the soil to be used.  Use a triple beam balance and record this weight on Data Sheet (A).
    2. Deposit a 1/4" layer of soil in the permeameter.
    3. Insert the 2" diameter footing in the vibrator, and apply the footing to the surface of the 1/4" layer until the entire surface appears to "tighten up."   All particles will appear to be firmly nested into the voids of the other particles.
    4. Repeat steps 2 and 3 until the permeameter is filled to within 1" of the top.
    5. The last layer should be put down in such a manner as to make the surface of the soil horizontal.  Check the surface of the soil at several points around the circumference with a steel scale.
    6. Weigh the pan and the remaining soil, and record the weight on Data Sheet (A).  The difference between this weight and the weight from 1 is the weight of the soil in the permeameter.  Record this weight on Data Sheet (A).
    7. Gently place a porous stone on the surface of the soil.
    8. Determine the length of the sample, L', between the two porous stones and record it on Data Sheet (A).
  2. 0% Relative Density
    1. Same as 1 for 100% Relative Density.
    2. Stand a wide mouth funnel in the permeameter, and pour enough material into the funnel to fill the permeameter to within an inch of the top.
    3. Slowly withdraw the funnel vertically while circling it around the inside of the permeameter, allowing the soil to flow from the funnel and fill the permeameter.
    4. Level the surface of the soil with a spatula until it is horizontal.  Be extremely careful in this operation so as to cause an absolute minimum of disturbance to the sample.
    5. Same as 6, 7, & 8 for 100% Relative Density.

5) Place a short length of brass spring on the top of the porous stone (approximately 1 1/2" long, with a modulus of 10 lb./in.) and attach the cover of the permeameter very carefully.  Be certain that the rubber gasket under the cover of the permeameter is well seated, to ensure the permeameter is air-tight.

6) The spring  being used will prevent any subsidence of the sample, particularly the looser ones, when water is moving through the sample.

7) Compute the total volume of the sample and record it on Data Sheet (A).

8) Compute the dry unit weight of the soil sample, and record it on Data Sheet (A).

9) Perform a sieve analysis on a 200g - 300g sample, following the procedure of Experiment 3.

10) Determine the maximum and minimum dry unit weights experimentally using a standard Proctor mold and following the procedures of steps 4A and 4B.

11) Compute the relative density of the soil sample and record it on the Data Sheet (A).

12) Connect the permeameter to the constant head supply tank.

13) Close the inlet, outlet, and piezometer valves.

14) Connect the vacuum line to the outlet valve of the permeameter and evacuate the permeameter for approximately five minutes.

15) While evavcuating the permeameter, check the various connections for leaks.

16) While evacuating, a specifc gravity determination can be started, following the procedures of Experiment 2.

17) At the end of the evacuation period, open the water inlet valve at the top of the permeameter and allow the water to flow in and saturate the sample under full vacuum.  As the advancing water reaches the botttom porous stone, close the bottom outlet valve so that no water is drawn into the vacuum line.

18) This evacuation and saturation procedure satisfies one of the two basic requirements of D'Arcy's Law, viz-a-vis, that 100% saturation exists in the sample under full vacuum.  Of course, the test must be performed using air-free water or this 100% saturation condition will not be maintained.

19) After closing the bottom outlet valve, open the piezometer valves which have already been connected to the piezometer tubes, and allow these tubes to fill.

20) Adjust the opening on the bottom outlet valve.

21) Allow the water to pass through the sample for approximately 5 minutes until steady-state conditions are achieved.

22) When the two water levels have come to rest, place a 250 ml graduated cylinder beneath the outlet, start a stopwatch, and collect water for 3 minutes.

23) Record: the two piezometer readings, h1 and h2; the quantity of water collected, q; and the time necessary to collect it, t, on Data Sheet (B).

24) Compute the hydraulic gradient, h/L, using h1 - h2 = h.

25) Compute the quantity q/At, and record the value on Data Sheet (B).

26) Determine the temperature of the discharge water and record it on Data Sheet (B).

27) Compute the quantity q/At at 20C and record it on Data Sheet (B).

28) Adjust the opening on the bottom outlet valve, thus changing q and h.  Repeat steps 20 - 27 a minimum of six more times.

 

1) Set up a cartesian plot with q/At at 20C as ordinate versus h/L as abcissa, and plot the values from steps 24 and 27 as they become available.  The best fit curve through the data will have a slope equal to k20.

2) Compute the absolute coefficient of permeability in cm2.

 

1) What is the degree of permeability according to Terzaghi & Peck's table of permeability values?

 

 

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